EPR paradox.

The Einstein-Podolsky-Rosen paradox is a thought experiment closely related to quantum entanglement: Two entangled particles are launched in opposite directions. From then on, the spin measured on one particle is related to the spin measured on the other instantly, even when they can't communicate. The correlations that appear after repeating the experiment follow a distribution that doesn't match classical predictions, but QM's predictions. As stated by Bell's theorem, there's no way to explain this behaviour using local hidden variables.

It's kind of weird that Einstein created this riddle after having found the solution, but we should be able to understand what's happening by now: Each carrier detected is at the same time the history of all the spacetime conditions that spanned from emission to detection. All carriers that appear spreading at c from entanglement event never “evolved”. They still feel connected to the entanglement event, no matter when/where they get detected in the universe. All these events reveal a correlated structure that would have manifested in a different way depending on the material world configuration and evolution. They match each other like pieces in a jigsaw puzzle, even if detections had happened any other way. Detections let observers deal with the entanglement event as if they were really there and then, so the entanglement event must tell the same history than all related detections, or reality would be inconsistent for the different observers.

The moment information about something spreads at any other velocity than c, it lose correlation with the original event. If a carrier could slow down just a bit for a moment, some amount of space and time would appear. It would get “detached” from the rest of carriers that go at c for that particular event, and it can't do anything to reach them again. From then on, it'll tell a story of causal relations, not instant quantum correlations.